The development and evaluation of Cryptophlebia Leucotreta granulovirus (CrleGV) as a biological control agent for the management of false codling moth, Cryptophlebia Leucotreta, on citrus
- Authors: Moore, Sean Douglas
- Date: 2003
- Subjects: Cryptophlebia leucotreta Cryptophlebia leucotreta -- Control Pests -- Biological control Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3942 , http://hdl.handle.net/10962/d1004001
- Description: A granulovirus isolated from Cryptophlebia leucotreta larvae was shown through restriction endonuclease analysis to be a novel strain (CrleGV-SA). No more than one isolate could be identified from a laboratory culture of C. leucotreta. However, a preliminary examination of restricted DNA profiles of isolates from different geographical regions indicated some minor differences. In surface dose bioassays on artificial diet, LC50 and LC90 values with neonate larvae were estimated to be 4.095 x 103 OBs/ml and 1.185 x 105 OBs/ml respectively. LT50 and LT90 values with neonate larvae were estimated to be 4 days 22 h and 7 days 8 h, respectively. Detached fruit (navel orange) bioassays with neonate larvae indicated that virus concentrations that are likely to be effective in the field range from 1.08 x 107 to 3.819 x 1010 OBs/ml. In surface dose bioassays with fifth instar larvae LC50 and LC90 values were estimated to be 2.678 x 107 OBs/ml and 9.118 x 109 OBs/ml respectively. LT50 and LT90 values were estimated to be 7 days 17 h and 9 days 8 h, respectively. A new artificial diet for mass rearing the host was developed. Microbial contamination of diet was significantly reduced by adding nipagin and sorbic acid to the diet and by surface sterilising C. leucotreta eggs with Sporekill. Almost 20 % more eggs were produced from moths reared on the new diet compared to moths reared on the old diet. A further 9 % improvement in egg production and a reduction in the labour required to produce eggs, was made with the development of a new oviposition cage attached to the moth eclosion box. Virus was mass produced in fifth instar C. leucotreta larvae by surface inoculating diet with the LC90. When 300 individuals were placed onto inoculated diet, 56 % of them were recovered six to 11 days later as infected larvae. Mean larval equivalents was 1.158 x 1011 OBs/larva. When larvae and diet were harvested together, highest yields of virus were achieved at eight days after inoculation. Microbial contamination in semi-purified preparations of CrleGV ranged from 176211 to 433594 (OB:CFU ratio). Half-life of CrleGV in the field was estimated to be less than 1 day on the northern aspect of trees and between 3 - 6 days on the southern aspect. Original activity remaining (OAR) of the virus dropped below 50 % after 5 days on the northern aspect of trees and was still at 69 % on the southern aspect of trees after 3 weeks. In field trials, CrleGV reduced C. leucotreta infestation of navel oranges by up to 60 % for a period of 39 days. CrleGV in combination with augmentation of the C. leucotreta egg parasitoid, Trichogrammatoidea cryptophlebiae, reduced infestation by 70 %. The integration of CrleGV into an integrated pest management (IPM) system for the management of C. leucotreta on citrus is proposed.
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- Date Issued: 2003
The biology of a facultative hyperparasitoid, Tetrastichus Howardi Olliff (Hymenoptera : Eulophidae), and its potential as a biocontrol agent of lepidopterous stem borers
- Authors: Moore, Sean Douglas
- Date: 1993
- Subjects: Eulophidae , Hymenoptera , Cephidae -- Biological control , Pests -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5649 , http://hdl.handle.net/10962/d1005331 , Eulophidae , Hymenoptera , Cephidae -- Biological control , Pests -- Biological control
- Description: The gregarious pupal endoparasitoid, Tetrastichus howardi Olliff (Hymenoptera: Eulophidae), was introduced into South Africa as a biocontrol agent against the maize and the sorghum stem borers, Busseola fusca Fuller and Chilo partellus Swinhoe. Preovipositional behaviour, ovipositional behaviour, development, fertility, sex-ratio, and longevity were studied in the laboratory. A complex courtship behaviour was observed, however 35.3% of females were mated before emergence from the host pupa. Preoviposition period ranged from 100 mins up to 5 days. Host searching time in Petri dishes was shorter for lepidopteran pupae than for their parasitoid pupae, and shortest when T. howardi had previously experienced the host. Duration of oviposition was significantly longer in the lepidopteran pupae than in the smaller tachinid puparia. T. howardi showed no difference in preference for hosts of different ages. The lepidopteran hosts were preferred to their parasitoids. If T. howardi had previously experienced a certain host its pereference for that host tended to increase, but not significantly. When reared on a certain host, the preference for that host did increase. The parasitoid was able to discriminate between parasitzed and unparasitzed pupae although this ability developed only 2 days after the pupa was parasitized. Cotesia sesamiae Cameron, the main indigenous parasitoid of B. fusca and C. partellus, was not attacked by T howardi. The total duration of development from egg deposition to the adult stage ranged from 18 to 26 days at 24°C and 60% RH. Emergence of adults began after first light, mean emergence time in winter being 09h00. Emergence rate of T. howardi from parasitized hosts, and mortality rate of parasitized hosts, was higher for C. partellus and H. armigera than for Eldana saccharina Walker and Palexorista laxa Curran. This decreased for C. partellus and H. armigera when superparasitized. A strong correlation existed between total parasitoids emerging from a host and percentage of females. When a lepidopteran pupa was parasitized by a single T. howardi female, 55 progeny emerged of which 94% were females. Larger females showed greater fertility and also produced a higher percentage of females. Younger hosts were more suitable for development of T. howardi. Females lived for 5.4 to 52.5 days, and males lived for 3.1 to 28.6 days, depending on presence or absence of food, water and hosts. Reasons for releasing T. howardi in the field are discussed. Only 2 recoveries of parasitized C. partellus pupae were made from the field.
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- Date Issued: 1993